The present application relates to kesterite-type semiconductor materials, and more particularly to a method of forming a film containing a Ag—Cu mixed kesterite compound for photovoltaic devices.
Kesterite-type semiconductors, Cu2ZnSn(S,Se)4 (CZTSSe), are promising semiconducting absorber materials for the next generation of thin film photovoltaic devices due to their suitable optical bandgaps that match well to the solar spectrum, high absorption coefficients, and earth-abundant elemental constituents. While photovoltaic devices fabricated from solution-grown CZTSSe have achieved a peak efficiency of 12.6%, further improvements have been stymied by an inability to increase the open circuit voltage, Voc, via processing optimization. Studies show that the open circuit voltage in CZTSSe-based photovoltaic devices is limited by absorber band tailing caused by high density of Cu/Zn antisites due to the similar ionic radii of Cu and Zn.
Substitution of Cu with an alternative element, Ag, is desirable since, in addition to belonging to the same chemical group as Cu, Ag possesses an atomic radius roughly 16% larger than that of Cu. The large dissimilarity in atomic radius is expected to suppress the Cu/Zn antisite defect formation. A method of forming a film containing a Ag—Cu mixed kesterite compound is thus needed.